Stem cell populations constitute only a small percentage of the total number of cells in the body, but are of immense interest because of their ability to repopulate the body. The longevity of stem cells and the dissemination of stem cell progeny are desirable characteristics. There is significant commercial interest in these methods because stem cells have a number of clinical uses. There is also medical interest in the use of stem cells as a vehicle for gene therapy.
Proteins and other cell surface markers found on stem cell and progenitor cell populations are useful in preparing reagents for the separation and isolation of these populations. Cell surface markers are also useful in the further characterization of these important cells.
Neural stem cells have been isolated from the adult subventricular zone (SVZ) and hippocampus (Gage, (2000) Science 287, 1433-38). These cells are an important source of new neurons, and offer the promise of novel central nervous system (CNS) repair therapies.
CNS stem cells are usually identified retrospectively by their ability to generate typical neurospheres or large adherent clones containing multiple neural cell types (Reynolds and Weiss, (1992) Science 255, 1707-10; Davis and Temple, (1994) Nature 372, 263-266; and Palmer et al., (1997) Mol. Cell. Neurosci. 8, 389-404), which precludes study of the initial stem cell population. Little is known about the unique biology of CNS stem cells, for example which specific gene products they express. Identification of “unique” gene products expressed by CNS stem cells would expand the understanding of these important cells, aid in their identification in vivo and enable their positive enrichment in vitro for study and use.
Two different cell populations have recently been identified as including SVZ stem cells: GFAP-expressing astrocytes (Doetsch et al., (1999) Cell 97 703-16; Doetsch et al., (1999) Proc. Natl. Acad. Sci. USA 96, 11619-11624) and Notch 1-expressing, ciliated ependymal cells lining the ventricles (Johansson et al., (1999) Cell 96, 25-34). These two distinct cell types are so intimately localized in vivo that it is difficult to separate them physically. Instead, defining specific features of stem cells will provide markers to help reveal their in vivo identity.
Genes expressed by adult CNS stem cells include Nestin, Musashi, Notch1 and GFAP (Sakakibara et al., (1996) Devel Biol. 176, 230-42; Johansson et al., (1999) Cell 96, 25-34; Doetsch et al., (1999) Cell 97, 703-16), but other CNS cell types also express these. Moreover, many of these markers are intracellular, limiting their usefulness for stem cell enrichment, although this problem can be overcome by creating transgenic mice with fluorescent reporter gene expression (Kawaguchi et al., (2001) Mol. Cell. Neurosci. 17, 259-273). A more generally useful marker would be a cell surface molecule allowing stem cell localization and purification from a wild-type mouse. Thus, there remains a need for tools, such as monoclonal antibodies that are useful in isolating and characterizing human non-hematopoietic progenitor and stem cells, and particularly central nervous system (CNS) neural stem cells and progenitor cells.